This invention relates to controllers for controlling the idle speed of an internal combustion engine and more particularly, to an improvement for such a controller.
U.S. Pat. No. 4,315,174 which issued Feb. 9, 1982, and is assigned to the same assignee as the present application, discloses an idle speed control actuator (ISCA) or idle speed controller. As disclosed in this patent, a pair of limit switches are utilized to indicate when an extendible and retractable member of the controller reaches the respective extended or retracted limit of its movement. These switches are incorporated in an electrical circuit for supplying power to a reversible d.c. motor which drives the member through an appropriate gear arrangement. The circuit is designed so, for example, when the member has reached its extreme extended position, the limit switch associated with this movement is open and this opens the circuit to prevent further application of power to the motor to drive the member in its extended direction. It does however allow application of power to the motor to drive the member in its retracting direction. The other switch operates in a similar manner. While the above design works in a satisfactory manner, there is the possibility of a limit switch not closing due to dust or similar particles preventing closure. In such happenstance, the movable member might reach an extreme position with both limit switches being open. If this does occur, it would be impossible to supply power to the motor to drive the motor in the opposite direction. What is needed, is a circuit by which the condition of both limit switches being open is sensed, but which enables the motor to be driven in the appropriate direction away from its extreme position if this condition does occur.